The wings of butterflies are covered with microscopic scales that give them their colour and also provide waterproofing. The wings of some species have large transparent areas through which the colour of the vegetation on which the butterfly has settled can be seen. Because they lack scales, these areas have poor waterproofing. The butterflies are eaten by birds.

a. Describe two selection pressures that are likely to control the size of the transparent areas of the wings of these butterflies.

b. In what circumstances might there be selection for larger transparent areas in the wings?